My understanding is the HNSCs are recommended because as this technet article states
This architecture is recommended to deploy sites because it is the same architecture that the Office 365 environment uses. Consequently this is the most heavily tested configuration. New features, including the App model and Request Management, are optimized for this configuration, and it is the most reliable configuration going forward.
However, are HNSCs required to take advantage of the App Model or is it a strong recommendation?
I've heard that they are required but I have not been able to find any documentation to back that up.